As shown in FIG. 1, a dual-purpose roller skate of the prior art comprises a bottom plate 1 which is attached to the underside of a main body (not shown in the drawing). The bottom plate 1 is provided in the underside thereof with two protrusions 2 corresponding in location to the toe portion and the heel portion of the bottom plate 1. The bottom plate 1 is disposed in an outsole 3 which is provided therein with two receiving cells 4 for receiving the two protrusions 2. Two roller sets 5 are fastened with the two protrusions 2 by a plurality of fastening screws. The roller sets 5 are formed of a fastening seat 6, a pivoting seat 7, and a wheel 8 which can be extracted from or retracted into the receiving cell 4. The two wheels 8 are extracted to enable the dual-purpose roller skate to be used as a roller skate. The two wheels 8 are retracted into the receiving cells 4 of the outsole 3 at such time when the dual-purpose roller skate is to be used as an ordinary footwear.
Such a prior art dual-purpose roller skate as described above is defective in design in that the outsole 3 is so thick as to accommodate the two roller sets 5 at the expense of the pliability of the outsole 3. In addition, the excessive thickness of the outsole 3 gives an added weight to the roller skate. Moreover, the extraction or retraction of the wheel 8 is done with finger which is apt to be soiled with dirt or even injured.